The script installs the cross compilers, which are used for building firmware. The sim is just a normal mac program so it doesn't need a cross compiler. The reason the script failed by the way is that you probably need to install gcc firat now that Mac OS no longer ships with it.

Edit: Sorry missed your last post. To build the UI Sim you may also need regular gcc for MacOS. I don't know if the built in LLVM compiler in xcode can build the sim without at least some makefile hacking.